On Wed, 28 Jan 2026 16:23:21 GMT, Damon Fenacci <[email protected]> wrote:
>> ## Issue >> >> This is a redo of [JDK-8361842](https://bugs.openjdk.org/browse/JDK-8361842) >> which was backed out by >> [JDK-8374210](https://bugs.openjdk.org/browse/JDK-8374210) due to C2-related >> regressions. The original change moved input validation checks for >> java.lang.StringCoding from the intrinsic to Java code (leaving the >> intrinsic check only with the `VerifyIntrinsicChecks` flag). Refer to the >> [original PR](https://github.com/openjdk/jdk/pull/25998) for details. >> >> This additional issue happens because, in some cases, for instance when the >> Java checking code is not inlined and we give an out-of-range constant as >> input, we fold the data path but not the control path and we crash in the >> backend. >> >> ## Causes >> >> The cause of this is that the out-of-range constant (e.g. -1) floats into >> the intrinsic and there (assuming the input is valid) we add a constraint to >> its type to positive integers (e.g. to compute the array address) which >> makes it top. >> >> ## Fix >> >> A possible fix is to introduce an opaque node (OpaqueGuardNode) similar to >> what we do in `must_be_not_null` for values that we know cannot be null: >> https://github.com/openjdk/jdk/blob/ce721665cd61d9a319c667d50d9917c359d6c104/src/hotspot/share/opto/graphKit.cpp#L1484 >> This will temporarily add the range check to ensure that C2 figures that >> out-of-range values cannot reach the intrinsic. Then, during macro >> expansion, we replace the opaque node with the corresponding constant >> (true/false) in product builds such that the actually unneeded guards are >> folded and do not end up in the emitted code. >> >> # Testing >> >> * Tier 1-3+ >> * 2 JTReg tests added >> * `TestRangeCheck.java` as regression test for the reported issue >> * `TestOpaqueGuardNodes.java` to check that opaque guard nodes are added >> when parsing and removed at macro expansion > > Damon Fenacci has updated the pull request incrementally with two additional > commits since the last revision: > > - JDK-8374582: fix comment layout > - JDK-8374582: fix constructor argument name Copyright years don't point to 2026 for the following touched files: src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp src/hotspot/cpu/x86/macroAssembler_x86.cpp src/hotspot/share/classfile/vmIntrinsics.hpp src/hotspot/share/opto/classes.hpp src/hotspot/share/opto/escape.cpp src/hotspot/share/opto/library_call.cpp src/hotspot/share/opto/library_call.hpp src/hotspot/share/opto/loopTransform.cpp src/hotspot/share/opto/loopopts.cpp src/hotspot/share/opto/macro.cpp src/hotspot/share/opto/node.hpp src/hotspot/share/opto/opaquenode.cpp src/hotspot/share/opto/opaquenode.hpp src/hotspot/share/opto/split_if.cpp src/java.base/share/classes/java/lang/String.java src/java.base/share/classes/java/lang/StringCoding.java src/java.base/share/classes/java/lang/System.java src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java src/java.base/share/classes/sun/nio/cs/CESU_8.java src/java.base/share/classes/sun/nio/cs/DoubleByte.java src/java.base/share/classes/sun/nio/cs/ISO_8859_1.java src/java.base/share/classes/sun/nio/cs/SingleByte.java src/java.base/share/classes/sun/nio/cs/US_ASCII.java src/java.base/share/classes/sun/nio/cs/UTF_8.java src/jdk.charsets/share/classes/sun/nio/cs/ext/EUC_JP.java.template test/hotspot/jtreg/compiler/escapeAnalysis/TestCanReduceCheckUsersDifferentIfs.java test/hotspot/jtreg/compiler/lib/ir_framework/IRNode.java test/hotspot/jtreg/compiler/unsafe/OpaqueAccesses.java ------------- PR Review: https://git.openjdk.org/jdk/pull/29164#pullrequestreview-3718529560
